Method and apparatus for recovering sugar



Oct 8, 1935. s. C.`MERED|TH ET AL 2,015,609

METHOD AND APPARATUS FOR RECOVERING SUGAR Filed Jan. 23, 1953 @MJ 6L,

7h27@ A T TORVN E Y Patented Oct. 8, 1.935

METHOD AND APPARATUS FOR RECOVERING SUGAR Sherman Chase Meredith, San Mateo,

Paul

Warren Alston, Concord, and Edward Taber` Winslow, Saratoga, Calif., assignors to Spreckels Sugar Company, San Francisco, poration oi.' California Calif., a cor- ApplicationJanuary 23, 1933, Serial No. 653,052

Claims.

Our invention relates to the recovery of sugar from solutions, and more particularly to improvements in the Steien" process of recover- 5 ing sugar from dilute molasses in the manufacture of beet sugar.

It is among the objects of our invention to increase the amount of lime-sugar compound precipitated by the presence of lime in a sugar solution.

Another object of our invention is to recover substantially all of -the sugar in solution by a single direct precipitation.

Still another object of our invention is to decrease the amount of lime needed in the process.

A further object of our invention is to increase the range of limes which may be employed, so that grades of lime which have previously been unsatisfactory may be used.

The invention possesses other iijects and features of advantage, some of which, with the foregoing, will be set forth in the following description of our invention. It is to be understood that we do not limit ourselves to this disclosure of species of our invention, as we may adopt variant embodiments thereof within the scope of the claims.

Referring to the drawing:

The figure of the drawing is a diagrammatical view showing the apparatus employed in carrying out the method of our invention.

The Steffen process is used in practically all American beet sugar factories for the purpose of recovering sugar from molasses. 'I'his process involves adding powdered quick lime to a dilute solution of the molasses. The lime reacts with the sugar in the solution to form an insoluble lime-sugar compound, known as saccharate, which precipitates from the solution. The limesugar compound is filtered from the mother liquur,` and after being washed is added to the raw beet juice, wherein it serves as a defecant. I n some installations employing the "Steiien process the ltrate obtained from the ilrst or direct precipitation is heated to precipitate a further amount of the lime-sugar compound. The additional precipitate is filtered oil from the mother liquor which is then discarded as waste water.

While the above process is accepted as the most practical and emcient, and is consequently widely used, it has certain inherent disadvantages. A In the first place, even with the best of regulated work and with the additional step of hot precipitation, the loss of sugar in the final waste water is at least 5% of the total sugar entering the process. In the second place, the amount of lime needed to precipitate the limesugar compound is excessive.

Another disadvantageof the Steiien process is that only certain grades of lime can be satisfactorily employed. This often necessitates the transporting of limestone for long distances when limestone deposits occur in the immediate vicinity. Among the other undesirable features of the Steffen process is that it requires several precipitations, involving special treatment and extensive apparatus.

The broad object of our invention is to eliminate the above mentioned disadvantages, by recovering practically all of the sugar which is now lost in the waste water; by decreasing the amount of lime required; by increasing the range of limes which may be satisfactorily employed; and by collecting all of the sugar recovered from molasses in one direct precipitation.

In terms of broad inclusion, the method embodying our invention relates to the addition of lime to a sugar solution so as to precipitate the lime-sugar compound, and comprises decreasing the size of the lime particles to increase the amount of precipitate. The apparatus for decreasing the size of the lime particles in the solution preferably comprises a system for circulating the mixture, and means in the system for breaking up the particles.

In greater detail, and referring to the ligure of the drawing, the apparatus embodying our invention comprises a suitable tank 2 for holding a dilute solution of the molasses from which the sugar is to be recovered. A main reaction tank 3 is provided and is connected to the supply tank 2 by a suitable duct 4. A valve 6 in the duct 4 provides means for controlling the introduction of the molasses solution into the reaction tank. A hopper I is also provided for holding a supply of powdered quick lime, and a discharge spout B is provided for introducing the lime into the solution of the reaction tank. 4 j

Means are preferably provided for agitating and circulating the mixture in the tank 3 for the purpose of thoroughly mixing the lime with the solution to promote the reaction between the lime and the sugar in the solution. For this ,0 purpose an impeller 9 is provided, and is mounted on a shaft II driven by a suitable motor I2. As an aid in mixing the lime With the solution,

a plate I3 is preferably mounted on the shaft I I below the discharge spout 8 for scattering the 5 lime over the surface of the fluid.

The reaction between the lime and sugar forms an insoluble lime-sugar compound, and in this form the sugar may be separated from the solution. This reaction however is accompanied by the evolution of considerable heat, and because of this factrsuitable cooling coils I4 are preferably provided in the tank for absorbing a portion of the heat.

The apparatus so far described finds its counterpart in the ordinary Steffen process, and consequently the elements thereof will not be treated in greater detail. It is understood that any other character or arrangement of apparatus for accomplishing the functions above described may be employed. y

In the Steffen process the fluid containing the precipitated lime-sugar compound is led directly from the reaction tank 3 to a filter where the precipitate is separated from the mother liquor. The precipitate is then washed and used as a defecant for the raw beet juice. Since the nltrate from this rst or direct precipitation still contains a comparatively large percentage of sugar it is ordinarily heated to cause further precipitation of the lime-sugar compound.

In the method and apparatus of our invention the mixture from the main reaction tank 3 is further treated before it is led to the rst filter, and the additional step of hot precipitation is omitted, Referring again to the figure of the drawing, a secondary reaction tank I6 is provided into which the contents of the main reaction tank 3 may be discharged through a suitable duct l1 having a Valve I8. The secondary reaction tank is provided with a suitable stirrer I9 driven by a motor 2| for mixing the contents thereof.

A circulating system is provided in connection with the tank I6, and preferably comprises a duct 22 leading from the bottom of the tank and discharging in the top thereof. Means are provided for circulating the contents of the tank I6 through the duct 22, and this is preferably accomplished by a pump 23 interposed in the duct 22 and driven by a suitable motor 24.

Means are provided in connection with the circulating system for breaking up the particles of free or uncombined lime carried in the liquid. For this purpose a grinder 26 driven by a suitable motor 21 is interposed in the duct 22. The grinder 26 may be any suitable means which will reduce the particles in the liquid to a finely divided state of subdivision. We have found that a colloid mill serves admirably for this purpose.

We have also used a gear pump with good results. In the latter case the pump 23 may be omitted, as the gear pump serves the dual purpose of reducing the size of the lime particles and pumping the mixture through the system.

A valve 2B is interposed in the duct 22 between its discharge end and the pump 23, and a duct 29 having a valve 3| and discharging into the filter 32 is connected in the circulating duct 22 between the pump 23 and the valve 28. With the valve 28 open and the valve 3| closed the mixture will be circulated through the duct 22, and with the valve 3| open and the valve 28 closed it will be pumped into the lter 32. I

It is understood that the tank I6 and the particular circulating system is shown merely for purposes of illustration. AAny other suitable apparatus for performing the function of breaking up the lime particles in the mixture prior to its delivery to the lter 32 may be employed.

In trial tests and with comparatively crude apparatus we were able to recover better than 99%' (and as high as 99.4%) of the sugar in the molasses. This represents a recovery of better than 5%v more of the sugar than it is possible to recover with the old Steffen process, and it is to be noted that this is effected without employing the fur- 5 ther step of hot precipitation. The elimination of the latter step is important becauseit represents a material saving of time, labor, equipment and expense.

A better idea of what the 5% saving means in 10 the manufacture of sugar is indicated by the following: About '7 lbs. of molasses is derived from each 100 lbs. of beets. The 7 lbs. of molasses contains about 31/2 lbs. of sugar. Consequently the saving in sugar per 100 lbs. of beets is equal to 15 5% of 31/2 lbs. or .175 lbs. This means that`approximately 3.5 lbs.' of sugar is saved per t0n (2000 lbs.) of beets. One plant with which We are familiar handles 475,000 tons of beets in a season. Our process will consequently effect a saving of 20 at least 1,662,500 lbs. of sugar per season at this plant alone.

Of course it is understood that the above calculations are on the basis of a 5% saving. Actu"A ally the saving effected by our process is greater. 25 The best average recovery of the old Steffen process, evenl with the additional step of hot precipitation, is from 93% to 95% of the actual sugar content of molasses. Since we are able to recover as high as 99.4% of the sugar, and this with crude' 3 0I amount of lime varying from 90% to 150% of the 4Q Weight of sugar. Unless the additional step of hot precipitation is employed the higher percentages of lime are required. In our tests, in which the large recovery of sugar was made in a single direct precipitation, we employed an amount of 46;:

lime which was only about of the Weight of sugar present in the molasses.

With less crude apparatus and with the close regulation maintained in commercial practice the amount of lime needed in our process will be 60 still lessened, and in all probability could be made to approach the theoretical requirement of about 49%. In commercial practice, however, the ideal amount of lime to be added is about 75% of the weight of sugar present in the molasses being 55 treated, because this amount of lime is that needed in the precipitate, either combined or uncombined, if the latter is to be used for defecating the raw beet juice in the preliminary steps of the beet sugar manufacture. ideal will be easily reached in our process.

In addition to effecting a saving in the amount of lime used over the old Sterren process, our improved process also increases the range of limes which may be employed. Limes have dif- 65- ferent characteristics, due to their different origin, and it is well known to those skilled in the art that the Steffen process is very critical with regard to the grades of lime employed therein. Unless limes having certain characteristics are 70 employed the amount of sugar recovered in the process is materially decreased. Consequently every beet sugar factory operating the Sterren process must exercise great care in selecting the lime, and many factories are forced-to transport Yo Without doubt this 60'- limestone for long distances when deposits of limestone occur in their own immediate vicinity. Our process is not so critical with regard to the nature and source of the lime employed, and consequently a greater number of the deposits of limestone become available in commercial practice.

There are various explanations which may be advanced as to the reason for the improved results of our process. It may be that in the old Steffen process a large portion of the lime particles became coated with a layer of the limesugar compound, and thus prevented the interior of the lime particles from coming into contact with molasses and thereby entering into the reaction. If this is true the act of breaking up the lime particles in our process would counteract this eiect. On the other hand, it may be that the reactivity of the lime is highly increased after its particles have been reduced to a nely divided state of subdivision.

Whatever the explanation may be, we have demonstrated that the reduction in size of the lime particles causes a direct precipitation of more than 99% of the sugar present in the molasses being treated. We have also demonstrated that the reduction in the size of lime particles eiTects a material saving in the amount of lime needed. Likewise We have demonstrated that a larger number of the sources of limestone become available for use in the manufacture of sugar when our process is employed.

We claim:

1. The method of increasing the amount of lime-sugar compound precipitated by the presence of lime in a sugar solution, which comprises treating the lime particles in said solution to disrupt the insoluble coating of lime-sugar compound forming thereon.

2. The method of recovering sugar from solution which comprises adding lime to the solution, and agitating the mixture while simultaneously breaking up the particles therein to expose substantially all the lime to reaction with sugar.

3. The method of recovering sugar from molasses which comprises diluting the molasses, adding lime to the molasses solution, and agitating the mixture While simultaneously breaking up the particles therein to expose substantially all the lime to reaction with sugar.

4. The method of recovering 'sugar from solution, which comprises adding lime to the solution, finely dividing the particles in the solution to expose substantially all the lime to reaction with sugar, and then filtering the mixture.

5. The method of recovering sugar from molasses, which comprises diluting the molasses, adding lime to the molasses solution, agitating the mixture While simultaneously breaking up the particles therein to a size to insure substantially complete reaction of the sugar with the lime, and filtering the mixture.

SHERMAN CHASE MEREDITH. PAUL WARREN ALSTON. EDWARD TABER WINSLOW. 

